Viewmaster question

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ericF's picture
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Viewmaster question

I'm having trouble getting the vertical deflection adjusted on my monitor when working in 80 column mode with a Viewmaster 80 (installed in a II+, slot 3). The top and bottom text lines extend beyond the physical screen dimensions. There are also faint vertical lines in 40 column mode. Otherwise, the card seems to work.

The normal 40 column output from the II+ appears fine. I've seen the deflection issue with two different monitors, but neither are "vintage".

Any ideas whether this is a problem with the board itself?

thanks,
eric

Update: //e enhanced works fine with this monitor in 80 column mode.

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dorkbert's picture
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Re: Viewmaster question

adjust monitor and call it done.

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Re: Viewmaster question

Unfortunately, I don't get much change with the monitor controls, or are you suggesting that I adjust the deflection internally?

The 80 column mode inserts an extra odd and even scan line between the rows of text. I don't think this is normal (certainly not compared to the //e in 80 column mode) but I don't have anything to compare it to.

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Re: Viewmaster question

Hello,

ericF wrote:
The 80 column mode inserts an extra odd and even scan line between the rows of text. I don't think this is normal (certainly not compared to the //e in 80 column mode) but I don't have anything to compare it to.

A picture would help.

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Re: Viewmaster question

Attached!

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Re: Viewmaster question

Every monitor is different. You might want to entertain the idea of adjusting a potentiometer inside that monitor to get what you are looking for.

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Re: Viewmaster question

I figured out my Videomaster 80 column card issue.

Like the Videx Ultraterm 80 card, the Viewmaster 80 uses a 6845 CRT controller (CTRC) to generate the timing signals of the display. The 6845 has 16 programmable internal registers and two read-only registers. The programmable registers can be set by writing the register number to $C0B0 and the desired register value in address $C0B1.

Mucking around with an oscilloscope and Seleae logic analyzer showed that all of the clock and timing signals were functioning properly in the card, and the output appeared normal other than extending beyond the physical screen dimensions. In all, the extra space I observed between character rows seems to be solely due to the default (power on) value of the R9 register, which sets the overall character height (the font plus extra space).

Scanning the card firmware shows that the default registers are written on start up beginning at $C82A. The values are stored in a table at $C88E:

Register - Description - Default value
R0 hoizontal total $7F
R1 hoizontal displayed $50
R2 horizontal sync position $62
R3 horizontal sync width $58
R4 vertical total $19
R5 vertical adjust $00
R6 vetical displayed $18
R7 vertical sync position $18
R8 interlace mode $00
R9 max scan line address $09
R10 cursor start $60
R11 cursor end $08
R12 start address (high) $00
R13 start address (low) $00
R14 cursor address (high) $00 (read / write)
R15 cursor address (low) $00 (read / write)
R16 light pen (high) read only
R17 light pen (low) read only

The default values of the registers for the "80-column video term emulation mode" given in the VidexUltraTermUM guide provide reasonably good results. I "optimized" these a bit:

Register - Description - Value
R0 hoizontal total $82
R1 hoizontal displayed $50
R2 horizontal sync position $68
R3 horizontal sync width $29
R4 vertical total $1C
R5 vertical adjust $08
R6 vetical displayed $18
R7 vertical sync position $1A
R8 interlace mode $00
R9 max scan line address $07
R10 cursor start $00
R11 cursor end $06
R12 start address (high) $00
R13 start address (low) $00
R14 cursor address (high) $00
R15 cursor address (low) $00

A simple "CTRC" program can change the card registers to these values:

0300- A2 00 LDX #$00
0302- 8A TXA
0303- 8D B0 C0 STA $C0B0
0306- BD 12 03 LDA $0312,X
0309- 8D B1 C0 STA $C0B1
030C- E8 INX
030D- E0 10 CPX #$10
030F- D0 F2 BNE $0302
0311- 60 RTS

312: 82 50 68 29 1C 08 18 1A
31A: 00 07 00 06 00 00 00 00

I'd like to burn my own EPROM at some point with these default register values to avoid having to enter them or run this program. I was also impressed by the Videx documentation. They provided firmware code, circuit diagrams and great descriptions of the card operation. The information was much more comprehensive than the AE documentation for the Videomaster card.

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Re: Viewmaster question

WOW!!!

Nice Trouble Shooting and Write Up!!

Where did you locate the Videx Documentation???

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Re: Viewmaster question

videx documentation is a part of the videoterm manual.

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Re: Viewmaster question

Yep. The Videx and Viewmaster manuals are on Asimov, Apple2Info.net and / or APPLE2.ORG.ZA.

The Videx manuals are great. Here's a good quote:

"For the casual user, not much need be said about the firmware that the board comes equipped with... If, however, you enjoy tinkering with register contents and other esoterica, this section will provide you with some very interesting Information."

Indeed!

If anyone has the circuit schematics of the Viewmaster card, I haven't been able to find them online. Is there an archive anywhere of Applied Engineering technical info beyond the user manuals?

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Re: Viewmaster question

no such doc exists for AE products. Most companies in the early 80s are pretty cool about releasing ROM listings and schematics. AE was not one of them.

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